Silicon (Si) photonics has become increasingly important in recent years, as Si is deemed to have great potential for augmenting the performance roadmap known as Moore's Law. As the short distance data transmissions rate approaches 10 Gb/s, usage of conventional copper interconnections has encountered challenges, such as increased power consumption, electro-magnetic interference, signal cross-talk, and heavier weight, which relegated usage of copper interconnections as an inferior approach for high bandwidth applications. To keep up with the ever need in up-scaling of bandwidth for interconnects, optical signal delivery is preferred (over electrical signal delivery) due to its high bandwidth and extremely low power consumption. Over the past decades, conventional optical components (for optical signal delivery) tend to be produced from III-V compound semiconductors, e.g. gallium arsenide (GaAs) or indium phosphide (InP), due to their excellent light emission and absorption properties. Unfortunately, compound semiconductor devices are generally too complicated to manufacture and costlier to implement in optical interconnects.
As a result, combining sophisticated processing techniques, with benefits in production costs and mass production ability, Si photonic has emerged as one of the most promising solutions for implementing the next generation of interconnections. However, the wavelength normally used for the majority of long-distance data transmission is in the 1.3 μm-1.55 μm range corresponding to the lowest loss window of the silica optical fiber. Beneficially, if the same said wavelength is utilized in future short-distance data transmissions including inter-chip, chip-to-chip and fiber-to-home communications, end users are then able to connect directly to external servers on the Internet, without need for wavelength conversion (typically performed bi-directionally for short-distance to long-distance data transmissions), thus enabling global communications to be much cheaper and easier. Although Si photo-detectors have been widely used in optical receivers in the wavelength range of 850 nm, its relatively large bandgap of 1.12 eV (corresponding to an absorption cutoff wavelength of about 1.1 μm) however hinders adoption of Si photo-detectors in the longer wavelength range of 1.3 μm-1.55 μm range. For a more seamless integration, a material with strong absorption coefficients in the 1.3 μm-1.55 μm range is thus desired.
Germanium (Ge), a Group IV material in the same group as Si, has attracted growing interest for realization of high performance photo-detectors due to its favourable absorption coefficient in the widely used telecommunication wavelength. However, Ge can be a challenging material to integrate in a CMOS environment due to its low thermal budget constraint, and its large lattice mismatch of around 4.2% with Si. Consequently, high defect densities in the Ge-on-Si epitaxial film may induce unfavourable carrier recombination that would degrade the detector quantum efficiency. In addition, in the case of p-i-n Ge photo-detectors, the diffusion of the p-type and n-type dopants into the intrinsic Ge also tends to be unavoidable during the Ge growth, resulting in unintentional doping of the intrinsic Ge region, which leads to unwanted degradation in electrical and optical properties of the p-i-n Ge photo-detectors.
One object of the present invention is therefore to address at least one of the problems of the prior art and/or to provide a choice that is useful in the art.